In both terrestrial and extraterrestrial environments, there are applications for devices constructed from a combination of components which are predominantly comprised of carbon. These applications arise from the desire to operate a system at temperatures which are considerably higher than those in which the system typically operates. For example, a component of a thrust-vectoring system for a rocket may be comprised of a metal which has acceptable mechanical properties so long as the temperature of the metal does not exceed some threshold. This may necessitate the use of a cooling system for the metal, whereas the cooling system could be eliminated if the metal were replaced with a more temperature-resistant material.
Carbon composites are known to have exceptional mechanical strength at high temperatures. However, carbon is susceptible to corrosion, oxidation, and erosion. Rhenium resists such effects and exhibits useful properties at such temperatures. However, in addition to being costly, rhenium has a relatively high density. High cost is undesirable in any application, and high density is particularly undesirable in aerospace applications.
Accordingly, considerable effort has been directed toward the replacement of metal components with rhenium-coated carbon components. Testing has shown that the forementioned corrosion, oxidation, and erosion can be minimized by applying a thin coating of rhenium on the composite by chemical vapor deposition (hereinafter, "CVD"). It has also been shown that rhenium can be diffusion bonded in the solid state. However, such bonding requires very high pressures. If performed on rhenuim-coated carbonaceous components the process tends to crack the components due to the brittle nature of the carbon composite, particularly where the components are relatively thin structures such as laminae. Moreover, such bonding requires that the components be maintained at a high temperature for a relatively long period of time. During that period, the diffusion of carbon into the rhenium causes embrittlement of the latter, which decreases load-bearing capacity to the extent that the rhenium layers may not survive the bonding process. An objective of the present invention is to provide a diffusion bonding process that overcomes these limitations.